Look for photoshop tutorials on youtube etc... Personally I would recommend playing around with an online editor like pixlr and just learn to use magicwand tool, color correction, and all the different effects available. Pretty much has everything you would need to make silly photoshops of various Rockets or DM. Hope that helps.
I'm no expert, but I assume the best way to learn Photoshop is the same as the best way to learn everything else: Practice, practice, practice.
Mess around with it, try and make goofy stuff, youtube... You have a lot of options. Personally, what got me in gear was making photoshops for clutchfans...
You mess around and eventually get better. There is no technique to learning it, everyone learns it their own way.
I'm a newbie to Photoshop too. I "purchased" it because I saw everyone on here doing some cool tricks with it. I just started fiddling around with it. When I wanted to do something that I didn't know exactly how to do I would just vaguely describe my intention in the google/youtube search bar and saw what would come up. I've only been using it a couple months you would be surprised at all the things you do over and over. You could just go to the library and check out a tutorial book too.
<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/NH0aEp1oDOI?fs=1&hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/NH0aEp1oDOI?fs=1&hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object> This blew my mind...
Start off with this video <object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/U_X5uR7VC4M?fs=1&hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/U_X5uR7VC4M?fs=1&hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object> Then proceed to go down the list http://www.youtube.com/user/MyDamnChannel#grid/user/D19BCF9D57320E03
I've always been pretty good with photoshop, but the new stuff that is coming out is leaving me in its wake. I think I could catch up pretty quick, but if your not working with it everyday it's tough to get everything down.
Iif you're a newbie there's always those effects packages you can download that have preset settings for various effects. That's what I used before I took the time to learn it.